Question

I need to compare two Dates (e.g. date1 and date2) and come up with a boolean sameDay which is true of the two Dates share the same day, and false if they are not.

How can I do this? There seems to be a whirlwind of confusion here… and I would like to avoid pulling in other dependencies beyond the JDK if at all possible.

to clarify: if date1 and date2 share the same year, month, and day, then sameDay is true, otherwise it is false. I realize this requires knowledge of a timezone… it would be nice to pass in a timezone but I can live with either GMT or local time as long as I know what the behavior is.

again, to clarify:

date1 = 2008 Jun 03 12:56:03
date2 = 2008 Jun 03 12:59:44
  => sameDate = true

date1 = 2009 Jun 03 12:56:03
date2 = 2008 Jun 03 12:59:44
  => sameDate = false

date1 = 2008 Aug 03 12:00:00
date2 = 2008 Jun 03 12:00:00
  => sameDate = false

Answer 1

Calendar cal1 = Calendar.getInstance();
Calendar cal2 = Calendar.getInstance();
cal1.setTime(date1);
cal2.setTime(date2);
boolean sameDay = cal1.get(Calendar.DAY_OF_YEAR) == cal2.get(Calendar.DAY_OF_YEAR) &&
                  cal1.get(Calendar.YEAR) == cal2.get(Calendar.YEAR);

Note that “same day” is not as simple a concept as it sounds when different time zones can be involved. The code above will for both dates compute the day relative to the time zone used by the computer it is running on. If this is not what you need, you have to pass the relevant time zone(s) to the Calendar.getInstance() calls, after you have decided what exactly you mean with “the same day”.

And yes, Joda Time’s LocalDate would make the whole thing much cleaner and easier (though the same difficulties involving time zones would be present).